1. Field of the Invention
The present invention relates to a phenolic chelate resin having a selective adsorbability to a heavy metal using a phenol, an aldehyde, and iminodiacetic acid.
More particularly, the present invention relates to a high adsorption capacity phenolic chelate resin having an adsorbability to a heavy metal in the proportion of at least 1.2 m equivalent per g. of dried terminal Na type resin.
2. Description of the Prior Art
Materials such as iminodiacetic acid which are capable of forming chelate compounds by coordination with heavy metal ions are well known and research on metal chelation has now been extended to various fields such as organic reagents for inorganic analytical chemistry, chelate titration, solvent extraction of metal ions, complex salt dyes, chelate pigments, and blocking agents for metal ions for use in the chemical industry. As amino acid type chelating compounds, there have been known various kinds of ethylene diamine tetracetic acid, trinitroacetic acid and the like other than the above iminodiacetic acid. Phenolic compounds substituted with iminodiacetic acid are also disclosed in Sallmann et al patent (U.S. Pat. No. 2,763,680).
However, the amino acid type low molecular chelate compounds tend to react with a metal, and are generally easily soluble in water. Especially, acids wherein the terminal group is neutralized with sodium are completely soluble in water. Therefore, the low molecular chelate compounds are not useful as one of the countermeasures for the pollution through the practical removal of heavy metals from drainage contaminated with heavy metals. Accordingly, there have already been made various trials for using the low molecular chelate compounds as an adsorbent for heavy metals by introducing a chelate group into a mother high molecular resin, which is obtained by converting the low molecular weight chelate compound into a water-insoluble and three-dimensional form, or for treating the chelate compound containing chelate group so as to make a three-dimensional marcromolecular form.
However, the introduction of a chelate group into a high molecular mother resin in a three-dimensional form, for example, the reaction of a phenolic resin with iminodiacetic acid and formaldehyde, is very difficult resulting in recovery of the greater part of iminodiacetic acid and reduction of the heavy metal-adsorbing property in the resin product to below 0.3 equivalent/g.
Since, in the latter case, the conventional procedure has various defects such as a low yield in the introduction into the aromatic ring of said iminodiacetic acid during the practical preparation thereof, and an insufficient regulation in the position of substitution within the aromatic ring of the iminodiacetic acid to be introduced or in the number of the iminodiacetic acid groups to be introduced into one aromatic ring, the successive macromolecule- forming and cross-linking step thereof cannot sufficiently be effected, thereby obtaining only a resin having an adsorbability to a heavy metal in the proportion of 0.3 to 0.8 m equivalent per g. of dried chelate resin but not a resin having an adsorbability in the proportion of at least 1.2 m equivalent, preferably 1.4 to 1.5 m equivalent which may be required from the commercial standpoint.
However, the kinds of commercially available chelate resins are very few since the chelating groups introduced into high molecular weight materials are generally poor in chemical stability as compared with ordinary ion-exchange groups such as a sulfonic group, a carboxyl group, and a quaternary ammonium group. This makes the reuse of such chelate resins difficult, the cost of the chelating group itself is high, and the procedure of introducing the chelating groups into high molecular weight materials is comparatively complicated, which results in greatly increasing the cost of the chelate resins as compared with ordinary ion-exchange resins.